Is a Diet High in Carbohydrate Appropriate for Humans?

This post comes out of some recent lively discussion on social media where I was challenged to re-consider my position that a low carbohydrate or very low carbohydrate (keto) diet can put people into remission of type 2 diabetes (T2D), but does not reverse it, and is not a cure. The discussion centred around whether some metabolic diseases such as T2D may come about as the result of us eating a diet that humans have not evolved to see, and whether eating a species-appropriate diet could be viewed as “curative”.


Back in 2018, I wrote my first article on the topic of whether a low carbohydrate diet actually “cures” type 2 diabetes, or puts it into remission.  In that article, titled The Difference Between Reversal and Remission of Type 2 Diabetes I wrote;

“Reversal” of a disease implies that whatever was causing it is now gone and is synonymous with using the term “cured”. In the case of someone with Type 2 Diabetes, reversal would mean that the person can now eat a standard diet and still maintain normal blood sugar levels. But does that actually occur? Or are blood sugar levels normal only while eating a diet that is appropriate for someone who is Diabetic, such as a low carbohydrate or ketogenic diet, or while taking medications such as Metformin? If blood sugar is only normal while eating a therapeutic diet or taking medication then this is not reversal of the disease process, but remission of symptoms.”

I argued that since type 2 diabetes is the result of beta cell failure, for someone to indeed be “cured”, there would need to be evidence of a restoration of beta cell function. 

In that article, I explained how in 2009 the American Diabetes Association defined the terms partial remission, complete remission and prolonged remission as follows;

  • Partial remission is having blood sugar that does not meet the classification for Type 2 Diabetes; i.e. either HbA1C < 6.5% and/or fasting blood glucose 5.5 – 6.9 mmol/l (100–125 mg/dl) for at least 1 year while not taking any medications to lower blood glucose.
  • Complete remission is a return to normal glucose values i.e. HbA1C <6.0%, and/or fasting blood glucose < 5.6 mmol/L (100 mg/dl) for at least 1 year while not taking any medications to lower blood glucose.
  • Prolonged remission is a return to normal glucose values (i.e. HbA1C  <6.0%, and/or fasting blood glucose < 5.6 mmol/L (100 mg/dl) for at least 5 years while not taking any medications to lower blood glucose.

Different studies, including those from the DiRECT diabetes remission trial and Virta Health define remission differently. The DiRECT diabetes remission trial defines remission as having a HbA1C below 6.5%, which is the cut-off for a type 2 diabetes diagnosis, as well as discontinuation of all diabetes medications for at least two months [1].  Virta Health, on the other hand defines remission in their studies as a HbA1C < 6.5% and fasting blood glucose ≤ 5.5 (100 mg/dl) while taking no medication, il with the exception of Metformin (or generic equivalent) [2].

There are 3 ways that are known for people to achieve remission of type 2 diabetes symptoms and these are;

  1. a low calorie energy deficit diet [1,3,4]
  2. bariatric surgery (especially use of the roux en Y procedure) [5,6]
  3. a ketogenic diet [2]

…but in each of these cases, we are defining remission in terms of the disease state and based on lab standards for defining normal cut-off values. That is, remission is defined as having normal fasting blood sugar and/or HbA1C, that are below the cut-off points for the disease, based on current diet.

This past weekend, I was appropriately challenged by someone on Twitter who said that this logic is flawed, because it assumes that the diet causing the disease is somehow natural. That is, if the diet causing the disease is unnatural, then couldn’t the natural diet indeed be viewed as curative?

I agreed to ponder this — and in fact, gave a great deal of thought to it. Several things came to mind that reinforced the idea that a high carbohydrate diet is not a “natural” human diet, and may not be appropriate for humans.

Human’s Evolutionary Diet

Over the course of man’s existence, there have been a number of major shifts in the human diet and with that change came the necessity of the body to adapt by producing enzymes capable of digesting and absorbing nutrients from these novel foods. This required the human genome (our genes) to adapt, evolve and change, and this type of adaptation takes a great deal of time [8].

There is good evidence for use of human-controlled fires which would have given us the ability to cook our meat, but is only about 800,000 years old [9] with less certain sites dating back 1,500,000 years [10,11].

The origin of domestication of animals is considered to be ~10,000 – 12,000 years and represents a relatively recent shift in the human diet — moving humans from being a hunter-gatherer species, to being an agricultural species [8]. The innovation of human agriculture not only greatly reduced diversity in the human diet, it resulted in an estimated 50%–70% of calories coming from starch (carbohydrates) [12].

According to Dr. Donald Layman, Professor Emeritus from the University of Illinois, looking at it from the perspective of man’s evolutionary history, the appearance of a diet centered around carbohydrates is very recent [9]. According to Dr. Layman, cereal grains as food were non-existent in the human evolutionary diet, and the same with legumes, such as chickpeas and lentils [13]. As well, refined sugar made up of sucrose was also non-existent in the evolutionary diet. While humans would eat wild fruit, these contained a fraction of the digestible carbohydrate content of domesticated fruitOn the rare occasion when humans came across a beehive and would eat honey (which is half glucose, half fructose), the idea of a diet high in sucrose and fructose was simply non-existent. According to Dr. Layman, consumption of dairy products and alcohol are also very recent in terms of human history [13]. We didn’t milk wild animals, we ate them and fermentation of fruit for wine is also very recent in terms of the evolutionary diet [13]. According to Dr. Layman if we look at contemporary agriculture, what has fundamentally changed is that these foods were totally non-existent in the history of man’s diet previous to the agricultural revolutionHumans did not evolve to see cereal grains, legumes, refined sugar, dairy foods and alcohol as human food and all of these are very rich in carbohydrate.  Interestingly, Dr. Layman stressed that the human body responds to dietary carbohydrate as if it were highly toxic, and that it must be rapidly cleared after eating in order for our body to maintain blood sugar within the very narrow range between 3.3-5.5 mmol/L (60-100 mg/dl).

Why would our body react this way?

According to Dr. Layman, over the span of human history we have developed very extensive and elaborate patterns for handling protein; for digesting and metabolizing it and have also developed a very high ‘satiety’ (feeling full) in response to eating protein, and that it is the only macronutrient that provides sufficiently strong feedback such that we can’t over eat it. He said that fat is a very passive nutrient and has very little direct effect on our body. We store it effectively and this ability to store excess intake as fat is what enabled us to survive as hunter-gatherers, but according to Dr. Layman, the macronutrient that is at odds in this picture is carbohydrate, simply because humans did not evolved to eat large amounts of carbohydrate.

Could it be that the diet that underlies metabolic disease like type 2 diabetes be one that is unnatural for humans? We certainly did not evolve to eat 300 grams of carbohydrate per day!

As I was contemplating this idea, I suddenly remembered seeing a video clip about a year or so ago that was mind-blowing to me at the time. It was of Dr. Walter Willett, Professor of Epidemiology and Nutrition at Harvard School of Public Health and a well-known advocate for diets very low in animal protein and high in carbohydrate (including the recent EAT-Lancet diet [14,15]) saying something along the lines that it is not the eating of dietary fat that makes people fat, but eating lots of carbohydrate.

Here is verbatim what Dr. Willett said;

 “There had been part of a belief that fat in the diet is what makes you fat and I even had colleagues who said that you can’t get fat eating carbohydrates because the body can’t convert carbohydrates to fat. I grew up in Michigan in a rural community and I can tell you that farmers have known for thousands of years if you want to fatten an animal a lot, what you feed them is grains, high carbohydrate diets, and you put them in a pen so they don’t run around and they get fat very predictably… most recent literature showed very clearly, you can really do randomized trials looking at weight change because you need just a hundred or few hundred people and you don’t need decades; you need a year or two and it’s very clear from those randomized trials that low-fat diets…ummm… fat is really not determinant of body weight. The percentage of calories from fat in the diet is not a determinant. In fact, lot of evidence suggesting it is easier for many people to get fat on a low-fat high carbohydrate diets. If anything, that’s what the literature is suggesting. So, it is interesting that fat in the diet just has almost nothing to do with fat in the body. We can get very fat on just lots and lots of carbohydrates.”

Lest anyone think I am taking the video clip out of context, here is the link to the full video from Willett’s keynote lecture from the 2012 Annual Advances in Cancer Prevention Lecture of July 25, 2012. The question and answer period which contains the clip above, begins 49 minutes into the full-length video.

So, it is well-known that eating lots and lots of carbohydrate can make pigs fat, and pigs are used in many research settings because of their similarities to humans. Is it not reasonable to deduce that humans eating lots and lots of carbohydrate can also make us fat?

But it’s not only are cereal grains and legumes that are relatively new in the human diet as food, but so are the oils extracted from cereal grains and seed, such as soybean oil and canola and that are in almost every manufactured food we eat.   

(I’ve previously written about concerns with these seed oils known as “polyunsaturated vegetable oils” in a two-part article from mid-2018 that can be read here and here.)

We, as humans have not evolved to eat these as food — and not only to eat them as food, but to eat them in HUGE quantities!

A study published in November 2018 in Metabolic Syndrome and Related Disorders reported that 88% of Americans are already metabolically unhealthy. That is, only 12% have metabolic health defined as have levels of metabolic markers “consistent with a high level of health and low risk of impending cardiometabolic disease“[16].

Metabolic Health is defined as ;

Waist Circumference: < 102 cm (40 inches) for men and 88 cm (34.5 inches) in women
Systolic Blood Pressure: < 120 mmHG
Diastolic Blood Pressure: < 80 mmHG
Glucose: < 5.5 mmol/L (100 mg/dL)
HbA1c: < 5.7%
Triglycerides: < 1.7 mmol/l (< 150 mg/dL)
HDL cholesterol: ≥ 1.00 mmol/L (≥40 mg/dL) in men and ≥ 1.30 mmol/L (50 mg/dl) in women

When looking at only 3 of the above 7 factors (waist circumference, blood glucose levels and blood pressure) more than 50% of Americans were considered metabolically unhealthy [16].

Given the slightly lower rates of obesity in Canada [17] as in the United States [18], presumably there is a slightly lower percentage of Canadians who are metabolically unhealthy, but the similarity of our diets may make that difference insignificant — which begs the question: what is it about our diet that results in 3/4 of us being metabolically unhealthy?

I believe the answer has something to do with the amount of refined carbs and refined fat that we eat together — something that was not part of our evolutionary history, and something that is now known to be irresistible.

Maybe the logic behind thinking about “remission” from diseases such as type 2 diabetes IS flawed because it DOES assume that our current human diet is “natural”. Genetic adaptation to dietary changes takes time, and in the context of human evolution, the foods that we eat so much of are relatively new.

Given this, is it not possible that some of the metabolic disease we as humans are facing in ever-increasing numbers might be related to us eating a diet that is not a natural human diet?

Could it be that consuming a diet that humans evolved to eat — and which reverses the symptoms associated with some metabolic diseases be indeed viewed as “curative”?

Definitely food for thought!

More Info?

If you would like more information about the different types of low carb or ketogenic diets I teach, please send me a note using the Contact Me form on the tab above.

To your good health!

Joy

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Reference

  1. Lean ME, Leslie WS, Barnes AC, et al. Primary care-led weight management for remission of type 2 diabetes (DiRECT): an open-label, cluster-randomised trial.  Lancet. 2018 Feb 10;391(10120):541-551. doi: 10.1016/S0140-6736(17)33102-1.
  2. Athinarayanan SJ, Adams RN, Hallberg SJ et al, Long-Term Effects of a Novel Continuous Remote Care Intervention Including Nutritional Ketosis for the Management of Type 2 Diabetes: A 2-year Non-randomized Clinical Trial.  preprint first posted online Nov. 28, 2018;doi: http://dx.doi.org/10.1101/476275.
  3. Lim EL, Hollingsworth KG, Aribisala BS, Chen MJ, Mathers JC, Taylor R. Reversal of type 2 diabetes: normalisation of beta cell function in association with decreased pancreas and liver triacylglycerol. Diabetologia2011;54:2506-14. doi:10.1007/s00125-011-2204-7 pmid:21656330
  4. Steven S, Hollingsworth KG, Al-Mrabeh A, et al. Very low-calorie diet and 6 months of weight stability in type 2 diabetes: pathophysiological changes in responders and nonresponders. Diabetes Care2016;39:808-15. doi:10.2337/dc15-1942 pmid:2700205
  5. Cummings DE, Rubino F (2018) Metabolic surgery for the treatment of type 2 diabetes in obese individuals. Diabetologia 61(2):257–264.
  6. Madsen, L.R., Baggesen, L.M., Richelsen, B. et al. Effect of Roux-en-Y gastric bypass surgery on diabetes remission and complications in individuals with type 2 diabetes: a Danish population-based matched cohort study, Diabetologia (2019) 62: 611. https://doi.org/10.1007/s00125-019-4816-2
  7. Evert, AB, Dennison M, Gardner CD, et al, Nutrition Therapy for Adults With Diabetes or Prediabetes: A Consensus Report, Diabetes Care, Ahead of Print, published online April 18, 2019, https://doi.org/10.2337/dci19-0014
  8. Luca F, Perry GH, Di Rienzo A. Evolutionary Adaptations to Dietary Changes. Annual review of nutrition. 2010;30:291-314. doi:10.1146/annurev-nutr-080508-141048.
  9. Goren-Inbar N, Alperson N, Kislev ME, Simchoni O, Melamed Y, et al. Evidence of hominin control of fire at Gesher Benot Ya’aqov, Israel.  Science.  2004;304:725–727
  10. Brain CK, Sillent A. Evidence from the Swartkrans cave for the earliest use of fire. Nature. 1988;336:464–466.
  11. Evidence for the use of fire at Zhoukoudian, China Weiner S, Xu Q, Goldberg P, Liu J, Bar-Yosef O Science. 1998 Jul 10; 281(5374):251-3.
  12. Copeland L, Blazek J, Salman H, Chiming Tang M. Form and functionality of starch. Food Hydrocolloids. 2009;23:1527–1534
  13. Layman, Donald, The Evolving Role of Dietary Protein in Adult Health, Nutrition Forum, British Columbia, Canada, June 23, 2013 https://youtu.be/4KlLmxPDTuQ
  14. The EAT-Lancet Commission on Food, Planet and Health,  https://eatforum.org/eat-lancet-commission/
  15. The EAT-Lancet Commission on Food, Planet and Health – EAT-Lancet Commission Brief for Healthcare Professionals,  https://eatforum.org/lancet-commission/healthcare-professionals/
  16. Araújo J, Cai J, Stevens J. Prevalence of Optimal Metabolic Health in American Adults: National Health and Nutrition Examination Survey 2009–2016. Metabolic Syndrome and Related Disorders Vol 20, No. 20, pg 1-7, DOI: 10.1089/met.2018.0105
  17. Statistics Canada, Health at a Glance, Adjusting the scales: Obesity in the Canadian population after correcting for respondent bias,  https://www150.statcan.gc.ca/n1/pub/82-624-x/2014001/article/11922-eng.htm
  18. State of Obesity, Adult Obesity in the United States, https://stateofobesity.org/adult-obesity/

 

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